1. Field of the Invention
The present invention pertains to particle accelerators and, more particularly, to a method and system for stabilizing the voltage at a terminal of a particle accelerator primarily during pulsed operation.
2. Discussion
When a high current, short duration pulse is produced from a particle accerator, the terminal voltage will drop to an extent sufficient to reduce undesirably the beam energy. For example, if a high current (5 amp), short duration (20 u sec.) pulse is produced from a high voltage (2 MeV) particle accelerator, the charge, .DELTA.q, is determined by the current, i, times the duration of the pulse, .DELTA.t, and is drawn directly from the high voltage terminal of the DC power supply of the particle accelerator. The power supply terminal voltage will accordingly drop by an amount, .DELTA.V=.DELTA.q/C.sub.T =i.DELTA.t/C.sub.T where C.sub.T is the terminal capacitance. The terminal capacitance, C.sub.T, is typically on the order of 100 to 200 pf, and the terminal voltage drop .DELTA.V will, thus, be 1000 KV for a C.sub.T of 100 pf and 500 KV for a C.sub.T of 200 pf. Consequently, the beam energy during the pulse will decrease by 50% and 25%, respectively, for these cases.
The beam energy change can be reduced by increasing the terminal capacitance; however, the size of the terminal required to increase capacitance sufficiently to materially reduce the voltage drop is prohibitive. For example, if the energy change, .DELTA.E, permissible during a beam pulse is 10 KeV, the terminal capacitance would be determined as C.sub.T =.DELTA.q/.DELTA.V=100.times.10.sup.-6 C/10.sup.4 V=10.sup.4 pf; and a terminal of this capacitance would have to be approximately sixty feet in length; it being also a function of diameter and spacing. Additionally, the energy, W, stored on such a terminal is W=1/2C.sub.T V.sup.2 =20,000 joules; a quite destructive stored energy level.